Police forces in the Democratic Republic of Congo have opened fire on thousands of protesters opposing President Joseph Kabila.

There were conflicting reports about the number of casualties with some opposition sources announcing a death toll of up to 15 at the Monday protest, in which police apparently fired real bullets and tear gas to disperse the demonstrators in the capital Kinshasa.

Protesters burned tires, blocking traffic at several main intersections in the Congolese capital where police in riot gear and armed presidential guards were stationed.

"The situation is very tense here. I have just taken a young person who had been hit by a bullet to hospital," said Martin Fayulu, from the Engagement for the Citizenry and Development (ECIDE) opposition party.

The protest was followed by a revised election law that would delay presidential and parliamentary polls beyond late 2016, allowing Kabila to remain in office.

The coalition opposition parties called on protesters to occupy the parliament building to stop passing any laws affecting the election.

Kabila has been the DRC president since 2001 and is serving a second five-year term as the elected president.